The present invention relates to freezers and refrigerators. More particularly the present invention relates to household and commercial freezers and refrigerators with multiple compartments: including freezing or frozen food compartments and refrigeration or fresh food compartments.
For most of refrigerators and freezers, a compression refrigeration system is the source of negative thermal potential. Compression refrigeration system consists of a compressor, a condenser, a metering/expansion device, and a low temperature evaporator installed in a freezing compartment. In refrigerators the refrigeration compartment is connected to the freezing compartment through the openings in the mullion or clearance between the mullion and the refrigerator case. Low temperature evaporator cools air in the freezing compartment. Refrigeration compartment is mostly cooled when cold air from the freezing compartment flows into the refrigeration compartment and cools the air in the compartment, although part of the cooling potential comes into the refrigeration compartment due to the heat transfer through the mullion. The air movement between the compartments is by forced or natural convection.
It is widely recognized, however, that the cooling of the refrigeration compartment by low temperature potential from the freezing compartment reduces the refrigeration capacity and efficiency. Also the air circulation between both compartments causes drying of the food in the refrigeration compartment and excessive frost building in the freezing compartment.
Some designers have attempted to overcome these problems by installation of two evaporators: a low temperature evaporator in the frozen food compartment and a high temperature evaporator in the fresh food compartment. There is no necessity for any clearance or openings in the mullion separating the compartments. Thus, there is no air circulation between the compartments. That eliminates moisture movement between two compartments and reduces consumption of electricity. Yet, because the refrigeration system provides much higher capacity to the high temperature evaporator, to sustain high efficiency this evaporator must be big in size with preferably forced air convection. Otherwise, the temperature of the evaporator drops down considerably, thus decreasing efficiency of refrigeration. In refrigerators with variable speed compressor high temperature operation requires low compressor speed. Still the evaporator has to have relatively large heat transfer surface. Another problem for refrigerators with two separate evaporators is the existence of temperature swings in the fresh food compartment. Unlike frozen food that has both latent and sensible heat, specific heat of fresh food itself consists only of sensible heat. It means that at the time when the compressor is off, the temperature in the refrigeration compartment quickly rises. On the other hand, the proper food preservation limits the temperature range for refrigeration. It causes excessive number of power switching of the compressor, which, in turn, reduces its efficiency and reliability. Even with extra insulation of the fresh food compartment, if the refrigerator door is open for some time, or somebody puts a new warm portion of fresh food and/or water into the compartment, compressor should start operating. In a refrigerator with variable speed majority of the time the compressor can run with low speed and jump the speed when the door is open. However, low speed operation is not very efficient, besides, in systems with the capillary tube as an expansion device changing of refrigerant flow rate causes reduction in the system efficiency. To overcome these problems some designers use a thermal storage in the fresh food compartment. However, known designs of a thermal storage for refrigerators are complicated and expensive.
In freezers and most of the contemporary refrigerators the biggest part of the negative thermal potential escapes through the walls and doors of the freezing compartment. Thus, in freezers and even in refrigerators that have two separate evaporators the increase of the low temperature operation efficiency is extremely important.
The present invention relates to freezers and different refrigerators. The preferred refrigerators, disclosed herein, are refrigerator-freezers that include side-by-side models with and without the ice/water dispenser in the door, models with the freezer mounted on the top or at the bottom of the refrigeration cabinet, and models with multiple compartments.